with every content management system, the question of what specs you need to run it always comes down to how much traffic you will have.
different content management systems will be more or less efficient, and may require different back-end processes to run.. so if you have a low end machine you might look for a more efficient, less-resource-intensive CMS, but you aren't going to find a simple answer, since the key factor is going to be how much traffic you have hitting your website.
